The present invention relates to an apparatus for reproducing video data spanning multiple storage media, and providing output on multiple channels.
Apparatus of this type is used in video-on-demand systems, in which a host device connected to a plurality of terminal devices supplies video programs requested by the terminal devices. The video programs are stored on disc media such as magneto-optical (MO) discs in a mass storage apparatus sometimes referred to as a jukebox. The apparatus also includes a plurality of drives for reproducing video data from the MO discs, and a mechanism for automatically transporting the discs between their storage locations and the drives.
Due to the limited storage capacity of the MO discs, a single video program may have to be stored on multiple discs. A known method of avoiding interruption of the reproduced picture while the MO discs are being changed is to record certain segments of the video data in a high-speed auxiliary storage device such as a magnetic hard disk drive. The auxiliary storage device stores a fixed-length segment leading into each MO disc, and these lead-in segments are reproduced from the auxiliary storage device while the MO discs are being changed.
The data access rate of even a high-speed hard disk drive is limited, however, so video data can be supplied from the auxiliary storage device to only a limited number of terminal devices at once. If this limited number of terminal devices are already being supplied with data from the auxiliary storage device when a further terminal device requires a change of disc, the auxiliary storage device is unable to reproduce the necessary lead-in segment, and the further terminal device experiences a temporary interruption of its video data. Depending on the length of the interruption, visual noise such as block noise may appear in the displayed picture, or the picture may freeze or go blank.
An object of the present invention is to prevent display impairments at changes of storage media in a video reproducing system.
The invention pertains to a video reproducing apparatus storing video data for a plurality of video programs on a plurality of removable media. At least some of the video programs span two or more of the removable media. The apparatus has a plurality of reproducing means for reproducing video data from the removable media, a transport means that automatically transports the removable media between their storage locations and the reproducing means, and a control unit. The control unit receives video program requests from a plurality of terminal devices, and controls the transport means and reproducing means so that each requested video program is reproduced and supplied to the requesting terminal device.
The invented method of controlling this apparatus comprises the steps of:
storing predicted times at which each video program currently being reproduced will require a change of removable media;
calculating the times at which a newly requested video program will require a change of removable media;
comparing the calculated times with the stored predicted times;
adjusting the calculated times according to the stored predicted times; and
storing the adjusted calculated times as the predicted times at which the newly requested video program will require a change of removable media.
In one aspect of the invention, the calculated times are adjusted so that all of the calculated times differ from all of the stored predicted times by at least a certain interval.
In another aspect of the invention, the apparatus also has an auxiliary storage means storing and reproducing lead-in segments for each of the removable media, and a switching means for supplying video data selectively from the reproducing means and the auxiliary storage means to the terminal devices. The calculated times are adjusted so that at most a predetermined number of lead-in segments are reproduced simultaneously.
By adjusting the times at which the removable media are changed, the invention prevents the transport mechanism and auxiliary storage means from being overloaded, and enables the terminal devices to receive video signals without interruptions at changes of media.